1. Field of the Invention
The present invention relates to a viscous fluid heater provided with a housing, which accommodates a heating chamber and a heat exchanging chamber, and a rotor that shears viscous fluid contained in the heating chamber to generate beat and exchange heat with circulating fluid contained in the heat exchanging chamber.
2. Description of the Related Art
Viscous fluid heaters, which are operated by the drive fore of automobile engines, have become widely used as an auxiliary heat source for automobiles. Japanese Unexamined Patent Publication No. 2-246823 describes a typical viscous fluid heater. The heater has front and rear housings that are fastened together by bolts, The coupled housings accommodate a heating chamber and a water jacket. Circulating coolant is drawn into the water jacket from an external heater circuit through an inlet port. The coolant in the water jacket is returned to the heater circuit through an outlet port. A drive shaft is rotatably supported in the front housing by bearings. A rotor, which rotates in the heating chamber, is fixed to the drive shaft. The walls of the heating chamber are provided near the rotor. Labyrinth grooves are defined in the walls of the heating chamber and in the outer surface of the rotor. The space between the heating chamber walls and the outer surface of the rotor is filled is viscous fluid such as silicone oil.
When the drive shaft is driven by the engine, the rotor rotates inside the heating chamber. The rotation of the rotor agitates and shears the viscous fluid located between the heating chamber walls and the rotor surface. This heats the viscous fluid. The heated viscous fluid exchanges heat with the coolant circulating through the water jacket. The heated coolant is then sent to the heater circuit to warm the passenger compartment.
In this prior art heater, there is a tendency for the rotor surface and the heating chamber wall to interfere with each other when increasing the heat generated during each rotation of the rotor.
In this type of heater, a belt transmits the drive force of the engine to the drive shaft by means of an electromagnetic clutch pulley or a pulley directly coupled to the drive shaft. Thus, when tension is applied to the belt due to changes in the engine speed or for other reasons, the tension is transmitted to the pulley. This inclines the axis of the drive shaft with respect to the ideal rotating axis and rotates the drive shaft in an inclined state. Furthermore, the perpendicularity between the drive shaft and the rotor, the parallelism between the rotor surface and the heating chamber wall, and the axial dimension of the heating chamber are not perfectly accurate. This is because of the dimensional margins that are allowed during production.
The rotor rotates and shears the viscous fluid most effectively when the dimension of the gap between the heating chamber wall and the rotor surface is one millimeter or less. Therefore, when the rotor rotates in an inclined state with respect to the heating chamber, interference occurs between the rotor surface and the heating chamber walls. This causes abrasion of the rotor surface and the chamber walls. To avoid such interference, the gap between the rotor surface and the heating chamber may be enlarged. However, this degrades the shearing effect of the rotor and decreases the heat generated during each rotation of the rotor.